More people than ever are using the London Underground; it handles around 4.8 million passenger journeys on a daily basis and 1.34 billion passengers annually. With the rise in public mobility and the need for people to keep in touch at all times, Transport for London (TfL) is under increasing pressure to provide mobile phone services on the London Underground for passengers, as well as for emergency services.
Indeed, TfL is reportedly in talks to provide mobile coverage for public safety communications. With underground locations such as the London tube network, which are heavily used by the public, robust wireless communication networks are critical for the provision of continuous communications during emergencies.
It is crucial that there is underground coverage for the TETRA two-way radio network for police, ambulance and fire personnel on the London Underground. However, its tunnel environment presents some significant challenges for radio distribution systems, which is holding back mobile operators from providing passenger and public safety communications underground.
Challenging radio environment
With 45% of the London Underground network in tunnels, this can present environmental and radio frequency (RF) challenges. Indeed, it is notorious for having a non-RF friendly environment. By virtue of the fact that much of the network is underground, receiving mobile or public safety signals can be nigh-on impossible.
The outdoor mobile network is simply not designed to penetrate subterranean spaces – and the ground literally acts as a radio wave shield, as radio signals from above simply cannot penetrate it.
Combine that with heavy construction materials, such as concrete and brick, and you have one of the most inhospitable mobile environments imaginable. Additional challenges are introduced by both changes in track elevation, and curves that radio waves are unable to bend around.
There are also the limitations with space in the tunnels and on the platforms. With 4.8 million passengers using the London Underground on a daily basis, it can get so overcrowded that the ability to gain access to the tunnels is extremely limited due to logistical and security issues – and finding available space and power for equipment can also be a real challenge.
This makes it difficult for mobile operators to install and maintain radio infrastructure. As such, they need to install equipment that will not only fit into small spaces, but that require little or no maintenance, as gaining access later can be an issue.
The tunnels in the London Underground are also known to collect dust and rubbish on a constant basis. While there are people who are employed to clean the tracks and tunnels to ensure safety on the London Underground and prevent dangers such as a fire, the dust and rubbish often clogs radiating cable, electronic equipment, fans and circuitry.
This can significantly affect the performance of RF distribution and requires constant maintenance in areas that are often hard to reach. As mentioned earlier, space limitations can cause logistical and security issues. Mobile operators should look at technology that can be sealed against dirt and dust, and therefore eliminate the need for constant maintenance.
Another challenge that mobile operators will be faced with when it comes to providing mobile services on the London Underground is that they must install technology that is able to deliver multiple services across numerous licensed RF bands, both mobile and public safety.
Indeed, mobile operators or transit authorities may require a shared radio distribution infrastructure in order to achieve efficiencies in both installation time and space requirements, as well as keeping costs low.
As such, mobile operators must use technology that is able to support multiple frequencies and that is able to be changed or upgraded without significant additional investment – not least because with the ever-changing wireless landscape and future rollout of next-generation services, such as 5G, this will be a critical requirement to meet future demands.
An underground-proof solution
Mobile operators require an underground-proof solution that is able to overcome the environmental and RF challenges that London’s tube network poses. By using small cell architecture, such as wideband distributed antenna system (DAS) technology, network engineers will be able to design a mobile network that is fit for the tunnel environment, while enhancing passenger and public safety communications underground.
Wideband DAS technology will extend wireless signal from a base station via discreet and remote antennas. Remote antennas can be deployed throughout the London Underground, which means that mobile operators will be able to provide the coverage and capacity required on the tube network.
In addition, wideband DAS solutions deliver uniform signal strength through the entire tube network because it can effectively distribute RF signals from a central radio source such as a base station through a fibre network to remote amplifiers directly adjacent to passive antennas. As such, since the signal is amplified end-to-end, the signal strength is the same at each antenna.
DAS antennas also fit well in environments where there is limited space, not least because the remote antenna units can be as small as a standard smoke detector. The antennas are also sealed off against environmental contaminants such as dirt and dust, which eliminates the cost and time involved in maintaining the equipment.
What’s more, wideband DAS technology can support multiple mobile operators and protocols, which means that they can provide access to major mobile services, such as 2G, 3G, 4G and eventually 5G, as well as public safety frequencies such as TETRA, within tunnels and on platforms.
The engineers for the London Underground would only need to deploy one set of wideband DAS electronics, which would be able to support multiple mobile operators, frequencies and services. As a result, deployment costs will be minimised and there will be minimal disruption to London Underground users.
Another benefit of using wideband DAS technology is that it can also be linked to local or remote base stations via fibre. This allows mobile operators to use existing fibre runs and RF resources to deliver the RF to the London Underground tunnel. This means that the base station can be located miles away from the DAS antenna and base station resources can be centralised to reduce CAPEX and OPEX.
Future mobile services on the London Underground
While the demand for mobile services on the London Underground is already high, with the rollout of next-generation services such as 5G and the number of passengers using the London Underground rising on a daily basis, the pressure only looks set to increase.
While passengers need and want mobile services on the London Underground, it’s also a matter of keeping passengers safe in emergencies. Public safety communications are a key driver behind TfL’s quest to provide mobile coverage and capacity on the London Underground.
Small cell architecture, such as a wideband DAS, will help mobile operators to overcome many of the challenges associated with tunnel environments that could have been holding TfL back from providing mobile services on London’s tube network. Ultimately, TfL will not only be able to provide a ubiquitous mobile service for its passengers, but for emergency service departments too.
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